Method for detecting stationary object on road

ABSTRACT

A method for detecting a target located above a road by using a camera and a radar system, wherein when it is determined that the target captured by the camera is the same target that has been captured by the radar, and when it is determined from an image captured by the camera that the target is at a height higher than road level, the method determines that the target is a stationary object located above the road. Further, when it is determined that the distance to the target captured by the camera or the radar is decreasing, and that the reception level from the target captured by the radar is also decreasing, the method determines that the target is a stationary object located above the road.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method for detecting astationary object located above a road, in particular, an overheadstructure such as a bridge over a road, by using radar detection incombination with camera image processing.

BACKGROUND ART

[0002] A scanning radar scans a radar beam by moving the beam from leftto right or from right to left at very small step angles within apredetermined time. At each step angle, the radar beam is projected fromthe radar-equipped vehicle toward a vehicle traveling in front, and thereflected wave from the vehicle in front is received and processed todetect the presence of the vehicle in front and compute the distance andrelative velocity with respect to that vehicle.

[0003] In the case of a radar, as the beam is usually scanned in lateraldirections as described above, it is difficult to obtain accurateinformation on height. As a result, when an overhead structure such as abridge over the road ahead or a structure such as a road sign located onthe roadside in front is detected, it may not be possible to distinctlyidentify whether the detected object is a stationary structure locatedabove the road or on the roadside in front or a vehicle traveling infront.

DISCLOSURE OF THE INVENTION

[0004] It is an object of the present invention to provide a method fordetecting a stationary object located above a road, which, when anobject is detected in the path in front, can identify whether thedetected object is a vehicle traveling in front or a structure, such asa bridge or road sign, located above the road or on the roadside infront.

[0005] According to the method of the present invention, the method usesa camera and a radar system, and when it is determined that the targetcaptured by the camera is the same target that has been captured by theradar, and when it is determined from an image captured by the camerathat the target is at a height higher than the horison level, the methoddetermines that the target is a stationary object located above theroad.

[0006] Further, according to the method of the present invention, whenit is determined that the distance to the target captured by the cameraor the radar is decreasing, and that a reception level from the targetcaptured by the radar is also decreasing, the method determines that thetarget is a stationary object located above the road.

[0007] According to the method of the present invention, when it isdetermined that the target captured by the camera is the same targetthat has been captured by the radar, and when it is determined from theimage captured by the camera that the height of the target, for example,the height above the road in the case of a road sign or the like, isequal to or higher than a predetermined value, the method determinesthat the target is a stationary object located above the road.

[0008] According to the method of the present invention, the method usesa camera system, and when it is determined that the length of a verticaledge or horizontal edge of the target captured by the camera isincreasing with time, the method determines that the target is astationary object located above the road.

[0009] The camera system comprises a multiocular camera or a monocularcamera. The method of the present invention determines that the twotargets are the same target when the difference between the distance Rgto the target captured by the camera and the distance Rr to the targetcaptured by the radar and the difference between an angle θg of thetarget captured by the camera and an angle θr of the target captured bythe radar are within a predetermined range.

[0010] When it is determined that the target is a stationary objectlocated above the road, data obtained from the target is deleted fromdata concerning a vehicle traveling in front.

ADVANTAGEOUS EFFECT OF THE INVENTION

[0011] According to the method of the present invention, sinceinformation about the height of the target, which cannot be obtained bythe radar system alone, is obtained from an image captured by the camerasystem, it can be determined in a simple manner whether the detectedtarget is a stationary object located above the road.

[0012] Further, according to the method of the present invention,whether the detected target is a stationary object located above theroad can also be determined in a simple manner by detecting a variationin the reception level obtained by the radar system.

[0013] Furthermore, according to the method of the present invention,whether the detected target is a stationary object located above theroad can also be determined in a simple manner from edge informationwhich is image information obtained from the camera system.

[0014] When the above methods are combined, it becomes possible todetermined in a simple and more reliable manner whether the detectedtarget is a stationary object located above the road.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a block diagram showing the configuration of an imagerecognition apparatus used in the method of the present invention.

[0016]FIG. 2 is a diagram showing the location of a structure above aroad in front and the variation of reception level when the structurebeing detected by a radar is an overhead bridge.

[0017]FIG. 3 is a graph showing how the reception level varies with theangle of a radar beam when the bridge is detected by the radar.

[0018]FIG. 4A is a diagram showing an image captured by a camera.

[0019]FIG. 4B is a diagram showing a range image created based ondistances measured by the camera.

[0020]FIG. 5 is a diagram showing an image captured by the camera when abridge 3 with a road sign attached to it is located in the path infront.

[0021]FIG. 6 is a diagram showing an edge image created by extractingvertical edges from the image shown in FIG. 5.

[0022]FIG. 7 is a diagram showing an edge image created by extractinghorizontal edges from the image shown in FIG. 5.

[0023]FIG. 8 is a flowchart illustrating a first embodiment of thepresent invention.

[0024]FIG. 9 is a flowchart illustrating a second embodiment of thepresent invention.

[0025]FIG. 10 is a flowchart illustrating a third embodiment of thepresent invention.

[0026]FIG. 11 is a flowchart illustrating a fourth embodiment of thepresent invention.

[0027]FIG. 12 is a flowchart illustrating a fifth embodiment of thepresent invention.

[0028]FIG. 13 is a flowchart illustrating a sixth embodiment of thepresent invention.

[0029]FIG. 14 is a flowchart illustrating a seventh embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030]FIG. 1 is a block diagram showing the configuration of an imagerecognition apparatus used in the method of the present invention. Inthe figure, reference numeral 10 is an image recognition part, and 20 isan application part. In the image recognition part 10, reference numeral13 is a radar, for example, a millimeter-wave radar, which detects thedistance, relative velocity, detection angle, reception level, etc. withrespect to an object located in the path in front such as a vehicletraveling in front. These pieces of information detected by the radarare input to an object recognizer 14. On the other hand, referencenumeral 11 is a camera system which, in the case of a multiocularcamera, comprises a plurality of cameras, for example, two cameras, thatare mounted spaced apart left and right on a vehicle in such a manner asto be able to capture an image in front of the vehicle. In the case of amonocular camera, a single camera is mounted on the vehicle in such amanner as to be able to capture an image in front of the vehicle. Imageinformation obtained from the camera 11 is supplied to an imageprocessor 12 where the image information is processed to obtaininformation on the distance, relative velocity, detection angle, height,width, etc. concerning the object located in front such as a vehicletraveling in front. These pieces of information are also input to theobject recognizer 14 where the information is processed to obtaininformation concerning the vehicle traveling in front, such as thedistance, relative velocity, etc. of the vehicle traveling in front.Information concerning an object located on the roadside or a structure,road sign, etc. located above the road in front can also be obtained atthe same time.

[0031] These pieces of information are input to a control ECU 21 which,based on the input information, controls the accelerator 22, brakes 23,steering 24, etc.

[0032]FIG. 2 is a diagram showing how a structure located above the roadin front is detected by the radar when the structure is, for example, anoverhead bridge. In the figure, reference numeral 1 is a vehicleequipped with the radar, 2 is a radar beam projected from theradar-equipped vehicle, and 3 is the bridge as the structure locatedabove the road in front. The graph in the lower part of FIG. 2 shows thereception level of the radar as a function of the distance from thebridge 3 to the vehicle 1. As shown by the graph, the reception leveldecreases as the vehicle approaches the bridge. Though not shown in thefigure, the reception level also decreases when the bridge is locatedmore than a certain distance away from the vehicle.

[0033]FIG. 3 is a graph showing how the reception level changes with theangle of the radar beam when the bridge 3 is detected by the radar asshown in FIG. 2. The radar beam 3 shown in FIG. 2 is scanned left andright in lateral directions at predetermined step angles; here, thereception level changes as the angle of the beam changes. When thetarget is a bridge as illustrated in FIG. 2, the reception level usuallychanges as shown by the graph in FIG. 3. More specifically, when thescan angle of the radar is plotted along the horizontal axis and thereception level along the vertical axis, since the bridge extendshorizontally, the reception level of the beam reflected by the bridge isthe highest when the beam is projected from the vehicle at a projectionangle of 0 degree, that is, in the straight forward direction, and thereception level decreases as the angle increases to the left or theright.

[0034]FIG. 4A is a diagram showing an image captured by the camera. FIG.4B shows a range image created based on distances measured by thecamera. By applying image processing to the signals captured by thecamera, information concerning the location of a particular object inthe image can be acquired. Furthermore, image edge information and rangeinformation can also be obtained. The edge information is obtained byextracting the points defining the boundaries between light and darkportions of the image, while the range information is obtained bycomparing the images captured by the multiocular camera and calculatingthe parallax between them.

[0035] Even in the case of an image captured by a monocular camera, edgeinformation can be obtained for pattern recognition, and the approximatedistance to the target object, the angle of its location, and theapproximate height of the object can be determined.

[0036]FIG. 4B is a diagram showing one example of the range image whenthe distance from the vehicle to the bridge is about 60 m and the fieldof view seen from the vehicle is 0°±20°. As shown, it can be seen fromthe image captured by the camera that the bridge is located at adistance of 60 m from the vehicle while the road surfaces in front areat 10 m and 15 m distances, respectively. The diagram shown here iscreated from the range image obtained by calculating the parallax overthe entire image. From this diagram it can be determined that the objectdetected about 60 m in front is an object located at a height higherthan the horizon level, and is not an object located on the road.

[0037]FIG. 5 shows an image captured by the camera when a bridge 3 witha road sign 4 attached to it is located in the path in front. FIG. 6shows an edge image created by extracting vertical edges from the imageshown in FIG. 5. As can be seen, when the vertical edges are extracted,only the vertical lines defining the supporting structure of the bridge3 and the sign 4 are shown in the image. The vertical edges becomelonger and move upward in the image as the vehicle approaches thebridge. FIG. 7 shows an edge image created by extracting horizontaledges from the image shown in FIG. 5. As can be seen, when thehorizontal edges are extracted, only the horizontal lines defining thesupporting structure of the bridge 3 and the sign 4 are shown in theimage. As in the case of the vertical edges, the horizontal edges becomelonger in the image as the vehicle approaches the bridge.

[0038] Embodiments

[0039] Next, embodiments of the present invention will be described withreference to flowcharts.

[0040]FIG. 8 is a flowchart for explaining a first embodiment. In thisembodiment, a multiocular camera is used as the camera. In S1, imageinformation obtained from the camera is processed in the image processorto calculate the range Rgm to the target, the angle θgm between thelocation of the target and the line of sight of the camera, and theheight Hgm of the target. On the other hand, in S2, the range Rrn to thetarget, the angle θrn of the radar beam reflected by the target, and therelative velocity Vrn with respect to the target are calculated from thesignal obtained by the radar. Then in S3, the range Rgm, angle θgm, andheight Hgm obtained by the image processing are cycled through an i(0-m)loop. That is, Rg, θg, and Hg are calculated in each cycle. Likewise,the range Rrn to the target, the angle θrn of the beam reflected by thetarget, and the relative velocity Vrn with respect to the target,obtained from the radar, are cycled through a j(0-n) loop. That is, Rr,θr, and Vr are calculated in each cycle. Next, in S4 and S5, it isdetermined whether the target captured by the camera is the same targetthat has been captured by the radar. First, in S4, the range Rgmobtained by the camera and the range Rrn obtained by the radar arecompared to determine whether the difference is within a predeterminedrange. If the difference is within the predetermined range (Yes), theprocess proceeds to S5. In S5, the angle θgm detected by the camera andthe angle θrn detected by the radar are compared to determine whetherthe difference is within a predetermined range. If the answer is Yes, itis determined that the target captured by the camera is the same targetthat has been captured by the radar, as the range Rg and angle θg of thetarget captured by the camera are approximately equal to the range Rrand angle θr of the target captured by the radar. Then, the processproceeds to S6 to determine whether the height Hg of the target capturedby the camera is higher than the horizon level. If the answer is Yes,the target is recognized as being an overhead structure, and the rangeRr to the target, the angle θr of the beam reflected by the target, andthe relative velocity Vr with respect to the target, obtained from theradar, are deleted from data concerning the vehicle traveling in frontso that these data will not be treated as the data concerning thevehicle ahead. That is, the data are deleted from the target data to beused for collision avoidance or vehicle-to-vehicle distance control, andthe loop is ended in S8. On the other hand, when the answer in any oneof steps S4 to S6 is No, the process also proceeds to S8 to end theloop.

[0041]FIG. 9 is a flowchart for explaining a second embodiment. In thisembodiment, a monocular camera is used as the camera. In S1, imageinformation obtained from the camera is processed in the image processorto calculate the approximate range R′gm to the target, the angle θgm,and the approximate height H′gm of the target. On the other hand, in S2,the range Rrn to the target, the angle θrn of the radar beam reflectedby the target, and the relative velocity Vrn with respect to the targetare calculated from the signal obtained by the radar. Then in S3, therange R′gm, the angle θgm, and the approximate height H′gm, obtained bythe image processing, are cycled through an i(0-m) loop. Likewise, therange Rrn to the target, the angle θrn of the beam reflected by thetarget, and the relative velocity Vrn with respect to the target,obtained from the radar, are cycled through a j(0-n) loop. Next, in S4and S5, it is determined whether the target captured by the camera isthe same target that has been captured by the radar. First, in S4, therange R′gm obtained by the camera and the range Rrn obtained by theradar are compared to determine whether the difference is within apredetermined range. If the difference is within the predetermined range(Yes), the process proceeds to S5. In S5, the angle θgm detected by thecamera and the angle θrm detected by the radar are compared to determinewhether the difference is within a predetermined range. If thedifference is within the predetermined range (Yes), it is determinedthat the target captured by the camera is the same target that has beencaptured by the radar, as the range R′g and angle θg of the targetcaptured by the camera are approximately equal to the range Rr and angleθr of the target captured by the radar. Then, the process proceeds to S6to determine whether the approximate height H′g of the target capturedby the camera is higher than the horizon level. If the answer is Yes,the target is recognized as being an overhead structure, and the rangeRr to the target, the angle θr of the beam reflected by the target, andthe relative velocity Vr with respect to the target, obtained from theradar, are deleted from the data concerning the vehicle ahead so thatthese data will not be treated as the data concerning the vehicle ahead.That is, the data are deleted from the target data to be used forcollision avoidance or vehicle-to-vehicle distance control, and the loopis ended in S8. On the other hand, when the answer in any one of stepsS4 to S6 is No, the process also proceeds to S8 to end the loop.

[0042]FIG. 10 is a flowchart for explaining a third embodiment. In thisembodiment, either a monocular camera or a multiocular camera may beused as the camera system. The flowchart shown in FIG. 10 is givenassuming the use of a multiocular camera. In S1, image informationobtained from the camera is processed in the image processor tocalculate the range Rgm to the target and the angle θgm and height Hgmof the target. On the other hand, in S2, the range Rrn to the target,the angle θrn of the radar beam reflected by the target, and therelative velocity Vrn with respect to the target are calculated from thesignal obtained by the radar. Further, in this embodiment, the receptionlevel Prn of the radar is calculated. Then in S3, the range Rrn to thetarget, the angle θrn of the beam reflected by the target, the relativevelocity Vrn with respect to the target, and the reception level Prn,obtained from the radar, are cycled through a j(0-n) loop. Next, in S4and S5, it is determined whether the target captured by the radar is astationary object or not. First, in S4, it is determined whether therange Rrn to the target captured by the radar is decreasing with time,that is, whether the radar-equipped vehicle is approaching the target.If it is approaching the target (Yes), the process proceeds to S5 todetermine whether the reception level is decreasing with time. As shownin FIG. 2, if the target is an overhead structure such as a bridge, thereception level decreases as the vehicle approaches the target.Therefore, if the answer is Yes, the detected target may be an overheadstructure such as a bridge, so that a stationary object candidate flagFrn is set (S6). Then, the process proceeds to S7 to cycle through ani(0-m) loop. On the other hand, when the answer is No in S4 or S5, theprocess also proceeds to S7. Next, the process proceeds to S8 to cyclethrough the i(0-m) loop and j(0-n) loop.

[0043] Next, in S9 and S10, it is determined whether the target capturedby the camera is the same target that has been captured by the radar.First, in S9, the range Rgm obtained by the camera and the range Rrnobtained by the radar are compared to determine whether the differenceis within a predetermined range. If the difference is within thepredetermined range (Yes), the process proceeds to S10. In S10, theangle θgm detected by the camera and the angle θrn detected by the radarare compared to determine whether the difference is within apredetermined range. If the difference is within the predetermined range(Yes), it is determined that the target captured by the camera is thesame target that has been captured by the radar, as the range Rg andangle θg of the target captured by the camera are approximately equal tothe range Rr and angle θr of the target captured by the radar. Then, theprocess proceeds to S11 to determine whether the height Hg of the targetcaptured by the camera is equal to or higher than a predetermined value.In this case, the predetermined value for Hg, by which the detectedtarget is judged to be an overhead structure or not, varies according tothe range Rg or Rr to the target. Accordingly, a map defining therelationship between Rgm or Rrn and Hgm is prepared, and thedetermination is made by referring to the predetermined value for Hgmcorresponding to Rgm or Rrn. If the answer is Yes, in this embodiment itis determined in S12 whether the stationary object candidate flag Frn isset or not. If the answer is Yes, the target is recognized as being anoverhead structure which is a stationary object, and the range Rr to thetarget, the angle θr of the beam reflected by the target, and therelative velocity Vr with respect to the target, obtained from theradar, are deleted from the data concerning the vehicle ahead so thatthese data will not be treated as the data concerning the vehicle ahead(S13). That is, the data are deleted from the target data to be used forcollision avoidance or vehicle-to-vehicle distance control, and the loopis ended in S14. On the other hand, when the answer in any one of stepsS9 to 12 is No, the process also proceeds to S8 to end the loop.

[0044] In the flowchart of FIG. 10 illustrating the third embodiment, asa multiocular camera is used, height Hgm is calculated in S1, and it isdetermined in S11 whether Hgm is equal to or higher than thepredetermined value. On the other hand, when a monocular camera is used,approximate height H′gm is calculated in S1, and it is determined in S11whether H′gm is equal to or higher than the predetermined value.

[0045]FIG. 11 is a flowchart illustrating a fourth embodiment. In thisembodiment, the radar system is not used, but only the camera system isused. The flowchart here is given assuming the use of a multiocularcamera. In S1, vertical edge length Lgm is calculated in addition to therange Rgm to the target, the angle θgm and height Hgm of the target.Then, in S2, it is determined whether Lgm is increasing with time. Ifthe answer is Yes, the target is recognized as being an overheadstructure, and the range Rgm to the target, the angle θgm of the beamreflected by the target, the height Hgm of the target, and Lgm, obtainedby the camera system, are deleted from the data concerning the vehiclein front so that these data will not be treated as the data concerningthe vehicle in front (S3).

[0046] The fourth embodiment can also be applied when a monocular camerais used. In this case, in S1, vertical edge length Lgm is calculated inaddition to the approximate range R′gm to the target, the angle θgm, andthe approximate height H′g of the target. Then, in S2, it is determinedwhether Lgm is increasing with time. If the answer is Yes, the target isrecognized as being an overhead structure, and the range R′gm to thetarget, the angle θgm of the beam reflected by the target, the heightH′gm of the target, and Lgm, obtained from the camera, are deleted fromthe data concerning the vehicle in front so that these data will not betreated as the data concerning the vehicle ahead (S3).

[0047]FIG. 12 is a flowchart illustrating a fifth embodiment. In thisembodiment, either a monocular camera or a multiocular camera may beused as the camera. The flowchart shown in FIG. 12 is given assuming theuse of a multiocular camera. In S1, image information obtained from thecamera is processed in the image processor to calculate the range Rgm tothe target, the angle θgm and height Hgm of the target, and verticaledge length Lgm. Then, the process proceeds to S2 to cycle through ani(0-m) loop. Next, it is determined in S3 whether Lgm is increasing withtime. If the answer is Yes, a flag Fgm indicating that the detectedtarget is a stationary object candidate is set in S4. Then, the processproceeds to S5 to cycle through the i(0-m) loop. Next, in S6, the rangeRrn to the target detected by the radar, the angle θrn of the radar beamreflected by the target, the relative velocity Vrn with respect to thetarget, and the reception level Prn of the radar are calculated. Then inS7, the range Rrn to the target, the angle θrn of the beam reflected bythe target, the relative velocity Vrn with respect to the target, andthe reception level Prn, obtained from the radar, are cycled through aj(0-n) loop. Next, in S8 and S9, it is determined whether the targetcaptured by the radar is a stationary object or not. First, in S8, it isdetermined whether the range Rrn to the target captured by the radar isdecreasing with time, that is, whether the radar-equipped vehicle isapproaching the target. If it is approaching the target (Yes), theprocess proceeds to S9 to determine whether the reception level isdecreasing with time. If the answer is Yes, the detected target may bean overhead structure such as a bridge as shown in FIG. 2, so that astationary object candidate flag Frn is set (S10). Then, the processproceeds to S11 to cycle through the j(0-n) loop. When the answer is Noin S8 or S9, the process also proceeds to S1. Next, the process proceedsto S12 to cycle through the i(0-m) loop and j(0-n) loop.

[0048] Next, in S13 and S14, it is determined whether the targetcaptured by the camera is the same target that has been captured by theradar. First, in S13, the range Rgm obtained by the camera and the rangeRrn obtained by the radar are compared to determine whether thedifference is within a predetermined range. If the difference is withinthe predetermined range (Yes), the process proceeds to S14. In S14, theangle θgm detected by the camera and the angle θrn detected by the radarare compared to determine whether the difference is within apredetermined range. If the difference is within the predetermined range(Yes), it is determined that the target captured by the camera is thesame target that has been captured by the radar, as the range Rg andangle θg of the target captured by the camera are approximately equal tothe range Rr and angle θr of the target captured by the radar. Then, theprocess proceeds to S15 to determine whether the height Hgm of thetarget captured by the camera is equal to or higher than a predeterminedvalue. If the answer is Yes, it is determined in S16 whether thestationary object candidate flags Fgm and Frn are set or not. If theanswer is Yes, the target is recognized as being an overhead structure,and the range Rr to the target, the angle θr of the beam reflected bythe target, and the relative velocity Vr with respect to the target,obtained from the radar, are deleted from the data concerning thevehicle in front so that these data will not be treated as the dataconcerning the vehicle in front (S17). That is, the data are deletedfrom the target data to be used for collision avoidance orvehicle-to-vehicle distance control, and the loop is ended in S18. Onthe other hand, when the answer in any one of steps S13 to 16 is No, theprocess also proceeds to S18 to end the loop.

[0049] In the flowchart of FIG. 12 illustrating the fifth embodiment, asa multiocular camera is used, height Hgm is calculated in S1, and it isdetermined in S15 whether Hgm is higher than the predetermined value. Onthe other hand, when a monocular camera is used, approximate height H′gmis calculated in S1, and it is determined in S15 whether H′gm is equalto or higher than the predetermined value.

[0050]FIG. 13 is a flowchart illustrating a sixth embodiment. Theflowchart here is given assuming the use of a multiocular camera. In S1,horizontal edge length Wgm is calculated in addition to the range Rgm tothe target, the angle θgm and the height Hg of the target. Then, in S2,it is determined whether wgm is increasing with time. In the case of aroad sign or the like, horizontal edge length increases as thecamera-equipped vehicle approaches it, as previously explained withreference to FIG. 7. Therefore, if the answer is Yes, the target isrecognized as being an overhead structure, and the range Rg to thetarget, the angle θg of the beam reflected by the target, the height Hgof the target, and Wg, obtained from the camera system, are deleted fromthe data concerning the vehicle in front so that these data will not betreated as the data concerning a vehicle in front (S3).

[0051] The sixth embodiment can also be applied when a monocular camerais used. In this case, in S1, horizontal edge length Wgm is calculatedin addition to the approximate range R′gm to the target, the angle θgm,and the approximate height H′g of the target. Then, it is determined inS2 whether wgm is increasing with time. If the answer is Yes, the targetis recognized as being an overhead structure, and the range R′gm to thetarget, the angle θgm of the beam reflected by the target, the heightH′gm of the target, and Wg, obtained from the camera system, are deletedfrom the data concerning the vehicle ahead so that these data will notbe treated as the data concerning the vehicle ahead (S3).

[0052]FIG. 14 is a flowchart illustrating a seventh embodiment. In thisembodiment, either a monocular camera or a multiocular camera may beused as the camera. The flowchart shown in FIG. 14 is given assuming theuse of a multiocular camera. In S1, image information obtained from thecamera is processed in the image processor to calculate the range Rgm tothe target, the angle θgm and height Hgm of the target, and horizontaledge length Wgm. Then, the process proceeds to S2 to cycle through ani(0-m) loop. Next, it is determined in S3 whether Wgm is increasing withtime. If the answer is Yes, a flag Fgm indicating that the detectedtarget is a stationary object candidate is set in S4. Then, the processproceeds to S5 to cycle through the i(0-m) loop. Next, in S6, the rangeRrn to the target detected by the radar, the angle θrn of the radar beamreflected by the target, the relative velocity Vrn with respect to thetarget, and the reception level Prn of the radar are calculated. Then inS7, the range Rrn to the target, the angle θrn of the beam reflected bythe target, the relative velocity Vrn with respect to the target, andthe reception level Prn, obtained from the radar, are cycled through aj(0-n) loop. Next, in S8 and S9, it is determined whether the targetcaptured by the radar is a stationary object or not. First, in S8, it isdetermined whether the range Rrn to the target captured by the radar isdecreasing with time, that is, whether the radar-equipped vehicle isapproaching the target. If it is approaching the target (Yes), theprocess proceeds to S9 to determine whether the reception level isdecreasing with time. If the answer is Yes, the detected target may be astationary structure such as a bridge as shown in FIG. 2, so that astationary object candidate flag Frn is set (S10). Then, the processproceeds to S11 to cycle through the j(0-n) loop. When the answer is Noin S8 or S9, the process also proceeds to S11. Next, the processproceeds to S12 to cycle through the i(0-m) loop and j(0-n) loop.

[0053] Next, in S13 and S14, it is determined whether the targetcaptured by the camera is the same target that has been captured by theradar. First, in S13, the range Rgm obtained by the camera and the rangeRrn obtained by the radar are compared to determine whether thedifference is within a predetermined range. If the difference is withinthe predetermined range (Yes), the process proceeds to S14. In S14, theangle θgm detected by the camera and the angle θrm detected by the radarare compared to determine whether the difference is within apredetermined range. If the difference is within the predetermined range(Yes), it is determined that the target captured by the camera is thesame target that has been captured by the radar, as the range Rg andangle θg of the target captured by the camera are approximately equal tothe range Rr and angle θr of the target captured by the radar. Then, theprocess proceeds to S15 to determine whether the height Hgm of thetarget captured by the camera is equal to or higher than a predeterminedvalue. If the answer is Yes, it is determined in S16 whether thestationary object candidate flags Fgm and Frn are set or not. If theanswer is Yes, the target is recognized as being an overhead structure,and the range Rr to the target, the angle θr of the beam reflected bythe target, and the relative velocity Vr with respect to the target,obtained from the radar, are deleted from the data concerning thevehicle in front so that these data will not be treated as the dataconcerning the vehicle in front (S17). That is, the data are deletedfrom the target data to be used for collision avoidance orvehicle-to-vehicle distance control, and the loop is ended in S18. Onthe other hand, when the answer in any one of steps S13 to 16 is No, theprocess also proceeds to S18 to end the loop.

[0054] In the flowchart of FIG. 14 illustrating the seventh embodiment,since a multiocular camera is used, height Hgm is calculated in S1, andit is determined in S15 whether Hgm is higher than the predeterminedvalue. On the other hand, when a monocular camera is used, approximateheight H′gm is calculated in S1, and it is determined in S15 whetherH′gm is equal to or higher than the predetermined value.

[0055] The present invention has been described by taking a bridge or aroad sign located above a road as an example of the stationary overheadstructure, but it should be understood that, in the present invention,the term stationary overhead object refers not only to theabove-mentioned structures but also to stationary objects such as a roadsign located on a roadside.

1. A method for detecting a stationary object located above a road byusing a camera system and a radar system wherein, when it is determinedthat a target captured by a camera and a target captured by a radar arethe same target, and when it is determined from an image captured by thecamera that the target is at a height higher than the horison level, themethod determines that the target is a stationary object located abovethe road.
 2. A method for detecting a stationary object located above aroad by using a camera system and a radar system wherein, when it isdetermined that a distance to a target captured by a camera or a radaris decreasing, and that a reception level from the target captured bythe radar is also decreasing, the method determines that the target is astationary object located above the road.
 3. A method for detecting astationary object located above a road as claimed in claim 2 wherein,when it is determined that the target captured by the camera is the sametarget that has been captured by the radar, and when it is determinedfrom an image captured by the camera that the target is at a heightequal to or higher than a predetermined value, the method determinesthat the target is a stationary object located above the road.
 4. Amethod for detecting a stationary object located above a road by using acamera system wherein, when it is determined that a vertical edge of atarget captured by a camera is increasing in length with time, themethod determines that the target is a stationary object located abovethe road.
 5. A method for detecting a stationary object located above aroad by using a camera system, wherein when it is determined that ahorizontal edge of a target captured by a camera is increasing in lengthwith time, the method determines that the target is a stationary objectlocated above the road.
 6. A method for detecting a stationary objectlocated above a road as claimed in claim 4 or 5 wherein, when it isdetermined that a reception level from a target captured by a radar isdecreasing, the method determines that the target is a stationary objectlocated above the road.
 7. A method for detecting a stationary objectlocated above a road as claimed in claim 6 wherein, when it isdetermined that the target captured by the camera is the same targetthat has been captured by the radar, and when it is determined from animage captured by the camera that the target is at a height higher thanroad level, the method determines that the target is a stationary objectlocated above the road.
 8. A method for detecting a stationary objectlocated above a road as claimed in claim 1, 2, 4, or 5, wherein thecamera system comprises a multiocular camera or a monocular camera.
 9. Amethod for detecting a stationary object located above a road as claimedin claim 1, 3, or 7, wherein it is determined that the two targets arethe same target when the difference between the distance Rg to thetarget captured by the camera and the distance Rr to the target capturedby the radar and the difference between an angle θg of the targetcaptured by the camera and an angle θr of the target captured by theradar are within a predetermined range.
 10. A method for detecting astationary object located above a road as claimed in claim 1, 2, 4, or 5wherein, when it is determined that the target is a stationary objectlocated above the road, data obtained from the target is deleted fromdata concerning a vehicle traveling in front.
 11. A method for detectinga stationary object located above a road as claimed in any one of claims1 to 10, wherein the stationary object located above the road is astationary object located above the road or on a roadside.